Improvements to the Image component

[dbismut]

This PR does the following:

• minor code fixes such as adding default values in parameters to reduce clutter, removal of unnecessary useCallback
• fix: allow overwriting of the style.position attribute
• fix: removal of the transition delay (this is debatable)
• feat: add onLoad prop to let users perform custom logic when the image loads
• feat: add usePlaceholder prop to allow for not showing the blurry placeholder
• feat: add the ability for users to pass a ref to the element

[dbismut]

I should add that unfortunately the ref commit kinda adds indentation to most of the code, which makes diffing a bit unpractical. I would suggest looking at each commit separately to better review the changes.

[stefanoverna]

Looking good! Thanks so much @dbismut, released as 1.6.9!